After gastrulation in sea urchins, identify the cells that remain on the surface.Multiple choice question.MesodermEctodermEndodermBlastocyst

Break Down the Problem

1. Identify the key phases of embryonic development, particularly after gastrulation.
2. Understand the different germ layers formed during this process: mesoderm, ectoderm, and endoderm.

Relevant Concepts

1. Gastrulation: A crucial developmental stage where the embryonic cells begin to differentiate into three primary germ layers.
2. Germ Layers:
   • Ectoderm: The outermost layer, which eventually forms the skin and nervous system.
   • Mesoderm: The middle layer, which forms muscles, the circulatory system, and other structures.
   • Endoderm: The innermost layer, which develops into the digestive tract and organs.
3. Blastocyst: An early stage of mammalian development that contains a fluid-filled cavity but is not applicable to sea urchins.

Analysis and Detail

• Following gastrulation, the ectoderm remains on the surface of the embryo. This layer contains cells that will later develop into the outer structures of the organism.
• The endoderm forms the internal structures, and the mesoderm lies between the ectoderm and endoderm.

Verify and Summarize

From the differentiation during gastrulation, we confirm that the ectoderm is the layer remaining at the surface, whereas the endoderm and mesoderm occupy inner positions.

Final Answer

Ectoderm is the correct answer, as it is the germ layer that remains on the surface after gastrulation in sea urchins.